Anal Incontinence is a problem which affects an estimated one million people in the United States today. Defined as the failure of voluntary control of the external anal sphincter, anal incontinence is a frequent and major problem in elderly individuals, yet is not limited to a specific population based on age. Incontinence is often a deleterious side effect of colonic and sphincter surgery; i.e., hemorrhoidal, colectomy and ulcerative colitis ideal pouch reconstruction, which sometimes results in the loss of control of the external sphincter muscle. When individuals become incontinent, the quality of their lives is decreased due to their inability to control normal bowel functions.
According to Gray's Anatomy (Gray, Anatomy of the Human Body, 1966), the two sphincter muscles of the anal region are the sphincter ani externus and the sphincter ani internus.
The sphincter ani externus, sometimes referred to as the external sphincter muscle, is composed of striated muscle fibers. The external anal sphincter is a cylinder of skeletal muscle supplied by the somatic nervous system and subject to voluntary control. The deeper portion of the muscle completely surrounds the anal canal. The superficial layer constitutes the major portion of the muscle, surrounding the end of the anal canal and encircling the anus. This muscle is always in a state of tonic contraction and, having no antagonistic muscle, keeps the anal canal and orifice closed.
The sphincter ani internus, or internal sphincter muscle, is composed of circular smooth muscle and is supplied by the autonomic nervous system, rendering it beyond voluntary control. The internal sphincter muscle is incapable of closing the anal canal and orifice.
Defecation in normal individuals is the result of reactions to local stimuli known as "defecation reflexes," and the relaxation of the external sphincter muscle. When fecal material enters the rectum causing distension of the rectal wall, the reflexes responsible for defecation are initiated. The fecal material is forced toward the anus by peristalitic waves in the descending colon, sigmoid, and rectum, accompanied by a decrease in the tonic constriction of the internal sphincter muscle. The movement of feces towards the anus usually results in an instantaneous contraction of the external sphincter muscle which temporarily prevents defecation. When the contraction of the external sphincter muscle is maintained, the peristaltic waves decrease as the rectum adapts to its new volume of material. The reflex waves will not usually return until an additional amount of feces has entered the rectum. However, when sufficient fecal material is already present in the rectum, voluntary contraction of the external sphincter muscle will not stop the increasing frequency of the peristaltic waves. These waves will continue until the fecal material has been eliminated, decreasing the distension of the rectal walls, and thus the defecation reflexes
The major difference in the defecation process between normal and incontinent individuals is the degree of control an individual has over his external sphincter muscle. Incontinence usually results from either an inability to voluntarily control the external sphincter muscle, or complete dysfunction of the muscle itself. The largest population suffering from anal incontinence is the aged, afflicted with generalized neurological disorders. A significant percentage of these individuals have normally functioning anal sphincter muscles, but become incontinent due to deficient cortical awareness of rectal filling.
Complete flaccidity and dysfunction of the external sphincter muscle will also result in anal incontinence. This can occur when the nerve impulses from the spinal cord are blocked. These impulses control the tone or residual degree of contraction in a skeletal muscle, such as the external sphincter. The severing of nerve impulses to the muscle reduces the skeletal muscle tone and ultimately leads to uncontrolled defecation.
In a high percentage of the cases, the inability of the individual to control the external sphincter muscle, due to either a neurological disorder or muscle dysfunction, will result in anal incontinence.
Electrical stimulation of normal skeletal muscles elicits a contraction response. Should the nerve impulses to a skeletal muscle be blocked, the individual cannot voluntarily control the muscle. However, the skeletal muscle will still respond to electrostimulation even though there is no physical connection between the muscle and the nerve impulses. This was successfully demonstrated in normal individuals by Wright et al., dealing with a specific skeletal muscle, the external anal sphincter. [Brit. J. Surg., pp. 38-41 (1985)]Subjects were injected with a spinal anesthetic agent designed to block the nerve impulses controlling the external sphincter muscle. Following the administering of the anesthetic agent, the subject showed no spontaneous electromyographic activity, indicating that the nerve impulses to the external sphincter had been completely blocked. Direct electrical stimulation was then applied to the external sphincter muscle producing a contraction of the muscle.
Similar work was performed by Collins, Brown, and Duthie again using continent subjects, blocking the neuromuscular junction with an anesthetic agent. [Scand. J. Gastroenterol., pp. 395-400 (1968)]When the electrical stimulation was applied, the external anal sphincter muscle contracted, closing the anal canal and the anus. Electrical stimulation caused the voluntary muscle to contract.
The work of C. Janneck with incontinent patients using direct electrical stimulation of the external sphincter muscle indicates that neurogenic anal incontinence can be successfully treated by direct stimulation of the anus. [Prog.-Pediatr.-Surg., pp. 119-139 (1976)]In the four subjects treated, anal continence was obtained in all cases following a course of daily treatment, lasting for approximately three months.
An intra-anal electrode was described by Hopkinson and Lightwood in 1966. [The Lancet, pp. 297-298 (1960)]Their research was a continuation of the work performed by Caldwell in 1963, who reported that direct electrical stimulation of the external sphincter muscle could be used to control anal incontinence. Hopkinson and Lightwood further demonstrated that the tone of the external sphincter muscle could be increased using continuous electrical stimulation administered via a rectally inserted plug. Based on their clinical research, the use of an energized anal plug was effective in providing anal continence. Rapid progress was made in improving the tone of the external sphincter muscle in cases where the muscle had become completely flaccid. It was the opinion of Hopkinson and Lightwood that progressively smaller diameter plugs could be used as the tone of the external sphincter muscle improved, and only occasional electrostimulation would be required to maintain continency.
Glen also found the intra-anal electrode plug to be an effective form of physiotherapy resulting in improved muscular tone. [J Pediatr. Surg., pp. 138-142 (1971)]Once voluntary control of the external sphincter muscle was achieved using electrostimulation, treatment would be discontinued briefly to evaluate the subject's progress toward unaided or spontaneous continence. Stimulation was required for shorter periods of time and for less frequent intervals to maintain continency during a course of treatment. The period of continuous electrical stimulation required to achieve control in the tested subjects varied from a period of weeks to several months. Glen concluded by recommending that electrical stimulation be employed as an aid to pelvic tone training as a treatment for incontinent individuals.
Van Der Mosel U.S. Pat. No. 3,749,100, discloses an electrostimulation probe comprising a suppository body formed with a rounded bulbous head, a reduced neck, and a broadened hilt, which is adapted to be inserted into the anus of a patient suffering from incontinence. The rounded bulbous tip and reduced neck facilitate anal insertion and subsequent retention. The rounded neck is clasped by the rectal sphincter, and is provided with a pair of spaced electrical contacts which rests against the sphincter. The broadened hilt limits insertion of the suppository body, and has a substantially flat base so as to permit the patient to sit or lie down comfortably with the device inserted. A pair of electrical leads are connected to the contacts, which are energized by a square wave signal having an average value of zero Volts, a peak potential not greater than 10 Volts and preferably between 1 and 2 Volts, and in the frequency range from about 18 to about 20 Hertz. Such electrostimulation is claimed to cause tonic and physiological contraction of the sphincter muscle, with significant results in the control of incontinence.
Stiebel et al, U.S. Pat. 3,403,684, disclose an electrical stimulator for supplying electrical stimulating pulses to preselected areas of the body. The stimulator comprises an elongated body having a bulbous portion at one end and a generally flat portion at the other end. The two end portions are interconnected by a generally narrow rod-like portion. A plurality of electrodes are formed on the bulbous end. In a preferred embodiment, the electrodes are spaced apart circumferential rings. The flat portion may contain a source of electrical energy and means for controlling the output of the device. The bulbous end contains a pulse timing circuit for controlling pulses of energy from the source of electrical energy to the plurality of electrodes.
Schaudinischky et al, Med. & biol. Engng. Vol. 7, pp. 341-343 (1969), describe shape conforming electrodes formed from flexible and elastic materials. In one embodiment, an electrode comprises a balloon-type elastic base with electrodes attached to the external surface of the balloon.
Geronimi-Stocker, Swiss Patent 206,545, describes an apparatus which can be inserted into the rectum of a patient. The apparatus comprises two electrodes. One electrode is adapted to contact the skin of the patient, and the other electrode is adapted to contact an organ to be treated.
Erlandsson, U.S. Pat. No. 4,106,511, describes an electrical stimulator for controlling the bladder and/or the rectal function. The stimulator comprises an expandable obdurator which is worn within the body. The obdurator is provided with electrodes which transmit a biphasic, pulsatile signal to the user.
Du Vall et al., U.S. Pat. No. 3,933,147, disclose an apparatus for treating disorders in the region of the pubococcygeous muscle. The apparatus comprises a probe having annular electrodes on the surface thereof. A pulsatile electrical signal is applied to the probe to stimulate the muscle.
Many of the devices described above are plug-like devices which operate by contracting the anal canal in the direction of its length, thereby closing the canal about the plug. It is an object of the present invention to provide a device which causes a contraction of the sphincter ani externus which closes the anal canal circumferentially.
Many of the prior art devices described above suffer from the disadvantage that once used, they must be cleaned before reinsertion. Additionally, in the case of rectal electrodes used to control incontinence, the electrodes must be removed and reinserted to permit defecation and reestablish continence, respectively. Continual removal and reinsertion can eventually lead to a physical deterioration of the electrode. Accordingly, it is an object of the present invention to provide a device for electrically stimulating the sphincter ani externus, which device utilizes an inexpensive, disposable electrode assembly which can be placed by a user over an anal probe body and easily removed therefrom, thereby eliminating the need to disinfect the electrodes between use, as well as the need to replace the entire device upon wear of the electrodes.
It is also an object of the present invention to provide a system for use in rehabilitating or training the sphincter ani externus, which system utilizes an electrical signal particularly adapted to aid in the restoration of voluntary control to this muscle. The system is adapted to contract the sphincter muscle by stimulating the muscle directly and by stimulating an afferent nerve which, by a spinal reflex, causes contraction of the muscle. The system is also adapted to stimulate a sensory nerve which enables the user to have a sensation and mental awareness of contraction.